The present invention relates to an optical transmission device and in particular to a parallel synchronous transmission device using a bundle of optical waveguides such as an optical fiber array, etc. and a transmission system using same.
Signal transmission techniques with a high speed and a high density are required in a computer or an exchange and transmission system. It is predicted that in electric signal transmission using coaxial cables or transmission paths utilized heretofore there is a limit in the speed and the density due to crosstalk, electric power consumption in transmission circuits, etc. On the contrary, an optical waveguide has in general a wide pass band and a low crosstalk. Further it is a light and fine line. In addition, there are no problems due to a grounding potential difference.
As described in Reference 1) K. Kaeda et al., "Twelve-channel parallel optical fiber transmission using a low drive-current 1.3 .mu.m LED array and a PIN PD array", Technical Digest of 1989 Optical Fiber Communication Conference, TUD3 and Reference 2) Y. Ota and R. G. Swartz, "Multi-channel Optical Data LINK (MODLINK)" Third Optoelectronics Conference (OEC'90) Technical Digest, 11D1-5, a plurality of signals are optically transmitted in parallel by means of an optical element array and an optical waveguide array which contrasts with to prior art transmission by means of one optical waveguide (optical fiber).
As described in the two references cited above, one of the most serious problems in a parallel transmission device consists in skew within an array. Reference 1) states that skew in a 12-channel 1 km multimode fiber (GI62.5) array is 8 ns. On the other hand, Reference 2) describes that skew within an array in a 12-channel multimode fiber (62.5/125GI) ribbon is 10 ns/km and that in practice skew compensation is necessary. In FIG. 1 of Reference 2), an optical deskewer is connected after a transmitter (Tx).
These prior art examples discuss skew within an array in a parallel transmission device (link array) using one fiber array or a fiber ribbon. According thereto, the number of channels in parallel in the array should be increased in order to increase the number of channels in parallel of signals. However there is a limit in the number of channels in parallel due to a limit in production.
Reference 2) deals with the possibility of extension. Since this system is characterized in skew regulation of an optical fiber for every channel, it is possible to increase the number of channels thereof by effecting skew regulation for all the channels. However, by this method, since the skew regulation is effected for every combination of fibers and transmitting-receiving modules, there are problems in productivity, maintenance, etc.
Conventionally, for example, Japanese patent publication JP-A 64-48011 discloses a parallel data transmission optical cable which performs parallel transmission of data at high speed between computers and between computer terminals using a plurality of optical fibers.